1. Field of the Invention
This invention relates generally to a fixed focus exposure control apparatus having a reverse spherical aberration corrective characteristic, and more particularly to, a fixed focus exposure control apparatus having a range responsive maximum effective aperture limiting shutter arrangement together with a reverse sperical aberration correcting lens for automatically maintaining a subject to be photographed at the forefront of its depth of the field.
2. Description of the Prior Art
Today there is a substantially large mass market for relatively low-cost cameras having automatic ranging systems. One camera of this type is commonly marketed by the Polaroid Corporation under the trade name "One-Step". This camera embodies a "scanning type" shutter blade arrangement used in conjunction with a fixed focus objective lens to provide a camera which is simple to operate. The camera also utilizes film units of the self-prossessable type which are automatically processed and ejected from the camera by way of a motorized drive mechanism. Thus, the photographer need only depress a single button to effect both the exposure and processing of the film units. Such cameras are generally focused for a fixed distance forward of the objective lens, as for example seven feet, so as to provide a maximum depth of field throughout an extended subject range. However, since the camera is fixedly focused at a determinate distance, the blur radius is at a minimum for photographic subjects located at the determinate focus distance and progressively increases as the subject is moved away from the determinate distance to which the lens is focused. Although the change in blur radius with camera-to-subject distance may not be readily apparent to the amateur photographer, it is obviously advantageous to minimize this change without sacrificing the simplicity adherent to a fixed focus objective lens.
Therefore, it is a primary object of this invention to provide a simple fixed focus camera wherein the blur radius is effectively minimized for photographic subjects located within a determinate camera-to-subject distance range extending from distances immediately adjacent the objective lens to infinity.
It is a further object of this invention to provide a fixed focus exposure control apparatus having a range responsive maximum effective aperture control shutter arrangement together with a lens arrangement embodying a reverse spherical aberration corrective characteristic which collectively operate to maintain the subject at the forefront of the depth of the field regardless of its actual distance from the camera.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.